Another steel question

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What is cold rolled steel supposed to look like? I ordered some kits from the James F Lincoln Foundation based on Jody saying in one of his videos that the kits were CRS. The quarter inch stock has a grey coating/layer on it. It is not thick and it zips off with a sander very quickly. The 1/8 inch stock looks almost like it has no coating but it does brighten up if you sand it. Acetone cleaning didn't change the appearance of either size coupons before sanding. I am guessing that the 1/4 inch stuff is HRS, and the 1/8 inch stuff is CRS?? I assume a sanding and cleaning with acetone is required before welding either of these?Original on the left (top), sanded on the right (bottom) (not sure why but my camera turned these sideways...not sure it matters)Miller Multimatic 255
Reply:I would say that you have some of each. Cold rolled has a very light coating, you can clean with a flap disc or Norton Blaze style pad, (I am a fan of these), Plenty of experts will tell you cold or hot rolled need no stripping with stick. I want fresh shiny metal showing. Hard abrasive disc, or Norton blaze type, (Generic is fine). Invest in the better 4-1/2" grinder. I have two Dewalts, one from Home Depot, the other from Airgas, They look similar, they are completely different. Most importantly, the cheap one ate my hand starting. It is awkward to grip, overcome the safety mechanism, and squeeze the trigger. It goes from 0 to 10,000 RPM in 1/1000000 second. It jumped out of my hand! The good one has soft start, it takes a second to come up to speed, no jump.In either event, be aware you only need to clean the surface where the filler touches. It isn't a big deal to grind that.
Reply:Originally Posted by Willie BI would say that you have some of each. Cold rolled has a very light coating, you can clean with a flap disc or Norton Blaze style pad, (I am a fan of these), Plenty of experts will tell you cold or hot rolled need no stripping with stick. I want fresh shiny metal showing. Hard abrasive disc, or Norton blaze type, (Generic is fine). Invest in the better 4-1/2" grinder. I have two Dewalts, one from Home Depot, the other from Airgas, They look similar, they are completely different. Most importantly, the cheap one ate my hand starting. It is awkward to grip, overcome the safety mechanism, and squeeze the trigger. It goes from 0 to 10,000 RPM in 1/1000000 second. It jumped out of my hand! The good one has soft start, it takes a second to come up to speed, no jump.In either event, be aware you only need to clean the surface where the filler touches. It isn't a big deal to grind that.
Reply:If you compare hot-rolled flat bar to cold-rolled, you'll find that in cross-section the hot-rolled has a slightly rounded edge.  The cold-rolled will have 90 degree edges and be more dimensionally exact.  Hot rolled flat bar:(----------------)Cold rolled flat bar:[---------------]
Reply:Originally Posted by GravelX2 on the steel.What is the model number of the slow start grinder? I have a Metabo like that but would like a cheaper alternative.
Reply:Thanks, Willie.GravelThe difference between theory and practice is that in theory there is no difference.